In many noise reduction systems, an input signal may be a combination of an interesting signal and unwanted noises. For example, in a crowded, noisy game room, a particular game player's voice may be regarded as the interesting signal, while other sounds in the game room are unwanted noises.
Under some existing techniques, single channel spectral subtraction may be used to produce an output signal with reduced noises. However, these techniques typically require distorting waveforms of input signals to remove the noises in the input signals. The integrity of the interesting signal under these techniques may be compromised as the waveforms comprising the interesting signal are distorted. In addition, to perform spectral subtraction reliably, many initial noise samples may have to be collected and processed to determine the characteristics of the interesting signal and the noises. As result, these techniques require a long adaptation time and may not be responsive to rapidly changing noise conditions. In applications with stringent timing requirement such as telecommunications and command-and-controls, these techniques may not be able to produce clean output signals in a timely manner for other related systems to perform related and subsequent operations such as voice recognition on the output signals.
In non-single-channel systems such as those using beamforming, multiple sensor elements may be spatially separated (e.g., at a half-wave-length) and form sensor arrays. Multiple input signals from a sensor array may be used to perform beamforming noise cancellation. However, these techniques typically require intensive calculations in order to form beams that may cancel noises from various sources. These techniques may also require determining magnitudes in input signals. Thus, like spectral subtraction systems, noise cancellation systems under these multi-channel beamforming techniques typically require a long adaptation time. If the sensitivities of the sensor elements vary, then the efficiency of the systems in noise cancellation may be further severely degraded.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.